A. Field of the Invention
The present invention generally relates to footwear and other foot-receiving devices. Aspects of the invention relate more particularly to impact-attenuating elements for articles of footwear or other foot-receiving devices.
B. Description of Background Art
Conventional articles of athletic footwear have included two primary elements, namely, an upper member and a sole structure. The upper member provides at least a partial covering for the foot that securely receives and positions the foot with respect to the sole structure. In addition, the upper member may have structures and a configuration that protect the foot and provide ventilation, thereby keeping the foot cool and removing perspiration. The sole structure generally is secured to a lower portion of the upper member and generally is positioned between the foot and the ground. In addition to attenuating ground reaction forces, the sole structure may provide traction and help control foot motions, such as pronation. Accordingly, the upper member and the sole structure operate cooperatively to provide a comfortable structure that is suited for a variety of ambulatory activities, such as walking and running.
The sole structure of at least some athletic footwear has exhibited a layered configuration that includes a comfort-enhancing insole, a resilient midsole (e.g., formed from a polymer foam material), and a ground-contacting outsole that provides both abrasion-resistance and traction. The midsole typically is the primary sole structure element that attenuates ground reaction forces and controls foot motions. Suitable polymer foam materials for the midsole include ethylvinylacetate or polyurethane that compress resiliently under an applied load to attenuate ground reaction forces.
One manner of reducing the weight of a polymer foam midsole and decreasing the effects of deterioration following repeated compression cycles is disclosed in U.S. Pat. No. 4,183,156 to Rudy, which patent is entirely incorporated herein by reference. In the Rudy construction, a fluid-filled bladder formed of elastomeric materials is provided. The bladder includes a plurality of tubular chambers that extend longitudinally along a length of the sole structure. The chambers are in fluid communication with each other and jointly extend across the width of the footwear. The bladder may be encapsulated in a polymer foam material, as disclosed in U.S. Pat. No. 4,219,945 (also to Rudy), which patent also is entirely incorporated herein by reference. The combination of the bladder and the encapsulating polymer foam material functions as a midsole. Accordingly, an upper member is attached to the upper surface of the polymer foam material and an outsole or tread member is affixed to its lower surface.
Bladders of the type described above are generally formed of elastomeric material and are structured to have upper and lower portions that enclose one or more chambers therebetween. The chambers are pressurized above ambient pressure by inserting a nozzle or needle connected to a fluid pressure source into a fill inlet formed in the bladder. Following pressurization of the chambers, the fill inlet is sealed and the nozzle is removed.
While such gas-filled bladders can be quite comfortable underfoot for the wearer, these bladders can lack the support or variance in support at different areas of the foot necessary for some activities, particularly athletic activities. Accordingly, there is a need in the art for impact-attenuating devices that provide a comfortable footbed while still providing adequate support and vertical deflection capabilities.